New x64 systems? Probably not. But since it still supports x86 and a whole slew of other architectures[1] still that don't always, it probably wouldn't make sense to stop.
Other commenter is correct, there are some late 486 boards with PCI support that would allow USB 1.0 or even 2.0 cards to be installed and used. Probably slow, but should work.
On the topic of modernizing a 486-class machine, there also exist a few with native PS/2 mouse support, and certain Matrox PCI cards have digital out, so it'd be possible to build a 486-class machine with USB 1.1, DVI/HDMI, and PS/2.
Since some Logitech wireless mice support PS/2, one could connect a 486 rig to a crisp digital LCD, use a wireless mouse, and plug in USB flash drives, sound, 10/100 network, NT 4.0, etc. -- all supported. Can make a fairly "modern" machine out of a pre-Pentium chip.
My CD backups lasted about 10-12 years before the silver started peeling off the discs :(
CD-RW/DVD+RW on the other hand are also even worse than flash in that regard and decay very quickly in my experience.
Old Systems. I have one such system that will is in line to move to 11.0 from 9.3. To do that I will boot from CDROM. It does not have any USB ports.
NetBSD is probably the only UN*X Type OS that can run on many of these 32 bit systems. Plus the NetBSD team is doing their best to support these old systems.
That saves me $ and helps the environment a little bit :)
Seems like a tradeoff with power though. Even emulating hardware from that era is more power efficient than actually running it. Of course, if you have custom ISA cards or something then you are likely stuck :)
I have done that in the past but there are already .img files specifically for USB. Seems redundant.